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Fix inconsistent space in `gui/control-panel` command help #6306

Job	Run time
lint / lint	28s
docs / Build linux64	1m 32s
test / Windows MSVC / Build win64	3m 51s
test / Linux gcc-12 / Build linux64	2m 5s
test / Linux gcc-11 / Build linux64	1m 43s
test / Run Linux test suite (gcc-12, all plugins) / Test (ubuntu, gcc-12, all plugins, default config)	1m 3s
test / Run Linux test suite / Test (ubuntu, gcc-11, default plugins, default config)	50s
test / Run Windows test suite / Test (windows, msvc, default plugins, default config)	1m 9s
test / Run Windows test suite (empty config) / Test (windows, msvc, default plugins, empty config)	4m 4s
	16m 45s

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